The invention relates to an apparatus for bracing electromechanical composite high-frequency oscillation systems (VFHS).
Low-frequency high-power ultrasound (NFLUS) is ultrasound with a working frequency of 15 to 200 kHz, preferably 15 to 60 kHz, for example 20 kHz, and a sound power of 10 W, preferably from 100 W to 20,000 W, for example 10,000 W. For example, piezo-ceramic or magnetostrictive systems are used to generate the ultrasound. Linear transducers and flat or curved plate transducers or tube resonators are known in the art. Low-frequency high-power ultrasound is used, inter alia, in the treatment of liquids, such as food, cosmetics, paints and nanomaterials. For this purpose, ultrasound is transmitted in liquids via a resonator with amplitudes of 1 to 350 μm, preferably 10 to 80 μm, for example 35 μm. Lambda is the wavelength resulting from the frequency and the NFLUS sound propagation speed in the high-frequency oscillation system. A high-frequency oscillation system can be composed of one or more Lambda/2 elements. A multipart high-frequency oscillation system having several Lambda/2 elements can be made from a single piece of material of appropriate length, or of a plurality of elements having a length n*lambda/2 (n ε N), which are assembled for example with screws. Lambda/2 elements may have various material cross-sectional geometries, such as circular, oval or rectangular cross-sections. The cross-sectional geometry and cross-sectional area may vary along the longitudinal axis of a Lambda/2 element. The cross sectional area may be between 0.01 and 300 cm2, preferably between 10 and 100 cm2, for example 50 cm2. Lambda/2 elements may be made, inter alia, from metal or ceramic materials or from glass, in particular from titanium, titanium alloys, steel or steel alloys, aluminum or aluminum alloys, for example from titanium grade 5. A Lambda/2 element may be manufactured from a single piece of material of appropriate length or may be made of a plurality of interconnected pieces of material.
High-frequency oscillation systems and Lambda/2 elements constructed from more than one piece of material may be joined in different ways to form a composite structure. A typical form of the composite structure is a high-frequency oscillation system that is compressed using a bracing element positioned in the center (FIG. 1). Piezo-ceramic composite high-frequency oscillation systems are composed of one or more Lambda/2 elements connected in the longitudinal direction, of which at least one Lambda/2 element has one or more piezoelectric ceramic elements, for example, disks, rings, disk segments or ring segments. Composite high-frequency oscillation systems with several piezo-ceramic elements, preferably with more than four piezo-ceramic elements, for example with eight piezo-ceramic elements, are used for low-frequency high-performance systems.
In particular, piezo-ceramic composite high-frequency oscillation systems require an increased surface pressure of the piezo-ceramic elements. This surface pressure may be between N 0.1 and 1000 N/mm2, preferably between 40 and 300 N/mm2, for example 100 N/mm2. The surface pressure has a significant effect on the efficiency, the maximum attainable ultrasonic power and the resonance frequency. Therefore, the surface pressure can be selected, inter alia, so as to maximize the efficiency and/or to minimize the thermal losses in the conversion of electrical energy into mechanical energy.
The surface pressure is produced by at least one bracing element, for example by a centrally positioned bracing screw.
Tensile loading of the bracing elements is produced which depends on the applied surface pressure. The tensile loading capacity of the individual bracing elements requires a minimum required sum of the material cross sections of the individual bracing elements. In the case of internal, e.g. centrally arranged bracing elements, the material cross-section of the bracing elements reduces the material cross-section of the ultra-sound-generating elements, e.g. the piezo-ceramic elements. The maximum diagonal length and thus the maximum attainable cross-sectional area of the ultra-sound-generating elements, such as the piezo-ceramic elements, are limited by the structure because with increasing length of the diagonal, both the tendency for destructive bending oscillations, for example of the piezo elements and pieces of material, increases and the heat dissipation increases due to an increased average distance to the uncovered surface of the ultra-sound-generating elements. Since the cross-sectional area of the ultra-sound-generating elements can thus not be chosen to be arbitrarily large, reducing the bracing elements, the required material cross-section of the bracing elements reduces the maximum possible cross-sectional area of the ultra-sound-generating elements.